This invention relates to a chargeable camera using a secondary battery.
Generally, in a photographing equipment using a secondary battery, a protection circuit for protecting circuits contained therein from overcharge or overdischarge is provided. A control circuit for the main body of a camera and a control circuit for charging of the secondary battery are separately formed and preset information items are exchanged between the circuits. For example, in a device using a secondary battery pack proposed in Jpn. Pat. Appln. KOKAI Publication No. 5-249537, a first CPU on the main body side of the camera and a second CPU on the secondary battery pack side are separately provided and the CPUs are constructed to control the camera and the charging operation of the secondary battery, respectively. If level signals of current values used which correspond to plural types of electrical load means are supplied to the second CPU, the second CPU controls the charging or discharging operation based on the level signal.
As one example of a protection circuit for preventing overcharge or overdischarge in the charging operation of the secondary battery, an overcharge protection circuit and overdischarge protection circuit constructed by using an overcharge detection comparator, overdischarge detection comparator and power MOSFET as is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-49181 are provided, for example. In this construction, each charge protection circuit and the control circuit for the equipment are separated from each other.
However, since the control means are respectively provided on the camera side and on the secondary battery side in the device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-249537, an additional circuit for making connection with them is required, and as a result, the scale of the device tends to become large. Further, if the load means and the charging means are simultaneously operated, there occurs a possibility that a large current flows from the external power source into the charging control circuit to damage the charging control circuit and others. Generally, dispersion in the operation voltages of the protection circuits will be finally determined by the precision of the parts constructing the device in many cases and the set value cannot be uniformly determined. Therefore, if an adjustment based on the uniformly determined value is made, the dispersion cannot be completely compensated for and it becomes more difficult to adjust the individual devices after the assembling and mounting processes.
As described above, in the conventional equipment and device using the secondary batteries, the circuit scale tended to become large, the mounting space became large and the cost of parts became high so that a reduction in the size and a lowering in the cost were automatically limited. Further, for the adjusting operation of the charging control section in the manufacturing process, it became necessary to adequately select constituent parts and make an optimum combination thereof. Further, since an adjustment after the mounting and manufacturing processes was difficult, the number of designing steps and the assembling cost for ensuring the precision of the product were increased accordingly. In addition, a design made by taking protection of the circuit provided for preventing overcharge or the like into consideration was required and the design tended to become complicated.
This invention has been made to solve the above problems and an object of this invention is to provide a camera using a secondary battery in which the cost can be lowered by realizing a camera in which the size is made small, the charging control circuit can be protected and the precision of a specified voltage of the protection circuit on the secondary battery side is made high, simplifying the design of the camera and simplifying the manufacturing process and adjustment after the manufacturing process.